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IC 9253 



BUREAU OF MINES 
INFORMATION CIRCULAR/1990 

¥92 



Review of Single-tntry Longwall 
Mining Technology in the United 
States 

By F. M. Jenkins and E. T. Cullen 




U.S. BUREAU OF MINES 
1910-1990 



THE MINERALS SOURCE 



%U OF * X * 



Mission: As the Nation's principal conservation 
agency, the Department of the Interior has respon- 
sibility for most of our nationally-owned public 
lands and natural and cultural resources. This 
includes fostering wise use of our land and water 
resources, protecting our fish and wildlife, pre- 
serving the environmental and cultural values of 
our national parks and historical places, and pro- 
viding for the enjoyment of life through outdoor 
recreation. The Department assesses our energy 
and mineral resources and works to assure that 
their development is in the best interests of all 
our people. The Department also promotes the 
goals of the Take Pride in America campaign by 
encouraging stewardship and citizen responsibil- 
ity for the public lands and promoting citizen par- 
ticipation in their care. The Department also has 
a major responsibility for American Indian reser- 
vation communities and for people who live in 
Island Territories under U.S. Administration. 



Information Circular 9253 



Review of Single-Entry Longwall 
Mining Technology in the United 
States 



By F. M. Jenkins and E. T. Cullen 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Manuel Lujan, Jr., Secretary 

BUREAU OF MINES 
T S Ary, Director 



Sy 



& 

* 



> 






-o 




Library of Congress Cataloging in Publication Data: 



Jenkins, F. Michael. 

Review of single-entry longwall mining technology in the United States / by 
F. Michael Jenkins and Elaine T. Cullen. 

p. cm. - (Bureau of Mines information circular; 9253) 

Includes bibliographical references. 

Supt. of Docs, no.: I 28.27:9253. 

1. Longwall mining-United States. I. Cullen, Elaine T. II. Title. III. Series: 
Information circular (United States. Bureau of Mines); 9253 

TN295.U4 [TN275] 622 s-dc20 [622'.334] 89-600381 

CIP 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Single-entry technology abroad 3 

Development 3 

Ventilation 5 

U.S. single-entry studies 6 

Sunnyside project 6 

Tunnel-boring machine project 9 

Other single-entry research studies in United States 15 

North American Mining Consultants study 15 

Ketron study 15 

Research related to single entries 16 

Conclusions 16 

References 17 

ILLUSTRATIONS 

1. Elevation and plan view of European-type single entry 4 

2. Sunnyside single-entry project 7 

3. Concrete crib line in 17th L single entry 9 

4. Single-entry center wall in 18th L, right side 10 

5. Single-entry center wall in 18th L, left side 10 

6. Elevation and plan view of Sunnyside split single entry 11 

7. Tunnel-boring machine 12 

8. Elevation and plan view of TBM split single entry 12 

9. Lower compartment of entry developed by TBM 14 



UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


cfm 


cubic foot per minute mt 


metric ton 


ft 


foot pet 


percent 


ga 


gauge st 


short ton 


in 


inch V 


volt 


kV»A 


kilovolt ampere 





REVIEW OF SINGLE-ENTRY LONGWALL MINING TECHNOLOGY 

IN THE UNITED STATES 



By F. M. Jenkins 1 and E. T. Cullen 2 



ABSTRACT 

Longwall mining systems are used to mine approximately 50 pet of the world's total underground coal 
production. Single entries are the predominant method of longwall development in Europe and Asia, 
where mining conditions are more severe than those encountered in the United States. During the 
1970's and early 1980's, the U.S. Bureau of Mines and the U.S. mining industry invested nearly $20 
million in single-entry and related research. This report reviews the accomplishments of single-entry 
research in the United States and describes two U.S. single-entry field projects: the Sunnyside single- 
entry project in central Utah and the tunnel-boring project in northern West Virginia. Also discussed 
are a single-entry study conducted by North American Mining Consultants (NAMCO) and a single- 
entry design study conducted by Ketron, Inc. This Bureau report compares the resulting technology with 
European counterparts to further assess the utility and efficiency of U.S. systems. 



J Mining engineer. 

information systems management analyst. 

Spokane Research Center, U.S. Bureau of Mines, Spokane, WA. 



INTRODUCTION 



Underground coal mines in the United States have used 
room-and-pillar methods of extraction almost exclusively, 
first employing the drill, blast, and load cycle and later 
using continuous mining machines. The room-and-pillar 
method of driving several parallel entries still dominates 
the layout of most coal mines. U.S. mining regulations 
evolved from experience gained in room-and-pillar mining 
and the use of multiple entries. Therefore, underground 
coal mining methods that employ different entry config- 
urations are constrained by regulations for room-and-pillar 
mining. For example, until the regulations were revised in 
1988, longwall mining was defined by the Code of Federal 
Regulations (CFR) as a special case of room-and-pillar 
mining (30 CFR 75.201-3, 1987) and hence was subject to 
laws governing that method. 

The U.S. coal industry currently mines underground 
seams where conditions are relatively favorable; that is, 
seams are thick, uniform, have few faults, and he under 
fairly shallow cover. Under these conditions, room-and- 
pillar and longwall mining methods result in relatively high 
production rates and favorable economic conditions. As 
easily recovered supplies are exhausted, however, U.S. 
mine operators will be forced to mine reserves where con- 
ditions are more severe, requiring new mining techniques. 
This is the case in Europe where longwall mining with 
single-entry development evolved as a method of handling 
severe mining conditions. 

Longwall mining was introduced into the United States 
as a means of increasing productivity. It was first tried at 
the turn of the century, but was abandoned because of the 
difficulty of manually moving timber support lines across 
the coal face. With the introduction of self-advancing 
mechanical props, longwall mining was tried again in Utah 
and West Virginia in the early 1960's. In Eastern U.S. 
coalfields, longwall mining was used in mines having 
ground control problems-ones with mudstone or friable 
shale roofs, which caved easily. Even though the cover was 
shallow, the mechanical props were too light, and these 
operations were not considered to be successful. Long- 
walls were then tried in seams with massive roof strata and 
shallow cover, again using light props. Under such condi- 
tions, the support either failed or was operated with great 
difficulty. As a result of these experiences, the growth of 
longwall mining in the East was stunted. At the same 
time, the Sunnyside Mines in Carbon County, UT, were 
among the first Western U.S. operations to use longwalls 
extensively in deep cover. These installations were suc- 
cessful; however, development-entry stability was a serious 
problem. 

In 1966, two longwalls were again tried in the East, one 
at considerable depth, under massive sandstone roof strata. 
Both were equipped with heavy-duty mechanical supports. 
Both longwalls were instantly successful, leading to the first 
modest expansion of the longwall mining system in the late 
1960's. Improvements in equipment and mining of thicker 
seams have accounted for dramatic increases in the pro- 
ductivity of longwall mining since 1980. 



Longwall mining offers several advantages over room- 
and-pillar mining. Carrying one long face and allowing the 
roof to break and cave behind the face simplifies roof 
control and ventilation problems, allows recovery of a 
higher percentage of the coal, increases production, and 
provides safer working conditions (I). 3 

Stresses created under deep cover can cause ground 
control problems for longwall operations, however. Long- 
wall operations at the Sunnyside Mines under 2,500 ft of 
overburden experienced stability problems in both head- 
gate and tailgate entries. Extreme roof and floor conver- 
gence, bumps, and bursting of the chain pillars forced the 
Sunnyside Mines to use a two-entry system to develop 
longwall panels. The mine continued using two entries to 
develop longwall panels under a "grandfather" clause in the 
Federal Coal Mine Health and Safety Act of 1969 even 
though three entries were required by the act. In spite 
of the double-entry development system, bumps and 
sloughing of the roof and ribs continued to be problems. 
In an effort to solve these problems, the company pro- 
posed experimenting with a single-entry development sys- 
tem under a cooperative research project with the U.S. 
Bureau of Mines. This proposal was accepted, and the 
first U.S. single-entry project began in 1971. 

In the same year, another cooperative research project 
was proposed to the Bureau by Eastern Associated Coal 
Corp. (EACC), Pittsburgh, PA, to drive a main devel- 
opment heading with a tunnel-boring machine (TBM). A 
TBM is a continuous excavation machine limited by its size 
and operation to excavating a single, circular-shaped entry. 
TBM's have been used worldwide for many years in such 
underground construction projects as transportation 
tunnels and watercourses. The TBM project, conducted 
from 1973 to 1979, had a purpose different from that of 
the Sunnyside project; however, both had an impact on 
single-entry research. Each project resulted in single 
entries being driven for development purposes. The TBM 
drove a main entry to reach a remote ventilation shaft, 
while the Sunnyside single entries developed production 
longwall panels. These two projects marked the beginning 
of single-entry research in the United States. By the first 
part of the 1980's, the coal industry and the Bureau had 
invested nearly $20 million in single-entry and related 
research. 

The main objective of this report is to document U.S. 
experience in single-entry research. This work was done 
in support of the Bureau's mission to improve the health 
and safety of miners in underground coal mines and to 
increase the productivity of those mines. The review 
begins with a look at single-entry coal mine development 
abroad. Much can be learned by comparing the equip- 
ment, methods, and regulations of other countries that use 
single entries with those of the United States, primarily 



Italic numbers in parentheses refer to items in the list of references 
at the end of this report. 



those used in the Sunnyside and TBM demonstrations. 
Both projects are reviewed to point out lessons learned 
from these experiences. 

This report does not deal with single-entry methods 
applied to other coal m inin g situations in this country, such 
as advancing longwall operations (2) and slope develop- 
ments (3-4). For example, in Mid-Continent Resources' 
L. S. Wood Mine in Pitkin County, CO, a single entry was 
developed as part of the longwall face. The entry was 
immediately separated into a double entry by a pumped 
pack wall and could be used as a panel for multilift 
longwall mining. The m inin g plan involved removing the 
top half of a 28-ft-thick coal seam with an advancing 
longwall and removing the remaining bottom half with a 



retreating longwall (5). Special situations such as this do 
not involve traditional in-seam single-entry excavations for 
coal reserve development. 

Two other sources of information are important to U.S. 
single-entry research. The first is a U.S. Department of 
Energy (DOE) contract report entitled "Single-Entry 
Longwall Study" (6) in which NAMCO, New York, NY, 
compared the pertinent mining regulations of other coal- 
producing countries to those of the United States. The 
second is a study of the design of a single-entry devel- 
opment system for retreat longwall m inin g systems by 
Ketron, Inc., Wayne, PA. It employed a systems-design 
approach that improved the in-seam divided single-entry 
concept used at Sunnyside. 



SINGLE-ENTRY TECHNOLOGY ABROAD 



DEVELOPMENT 

Longwall mining has been the rule rather than the 
exception for many years in the major coal-producing 
countries of Europe. This is a result of the conditions 
encountered as shallow coal reserves were exhausted and 
mining moved to deeper workings. European (which in- 
cludes British) coalfields generally he in thinner beds and 
at greater depths than U.S. deposits currently mined. 
Depths of 3,000 to 4,000 ft are common, and much greater 
ground pressures are experienced than in this country's 
coal mines. 

In Europe, both advance and retreat longwall mining 
are practiced. In advance longwall mining, the entry or 
entries used to access the face may be driven with the face 
or ahead of the face. These entries must remain open 
throughout mining of the panel to provide haulage, 
ventilation, and escapeways. For retreat longwall mining, 
a coal block is defined by the complete driving of the 
entries before the face equipment is installed. The face is 
then mined back toward the haulage main, allowing the 
roof to cave behind. In either advance or retreat systems, 
if longwall panels are to be developed consecutively across 
a coal block, the entries will be used for two panels 
(headgate for one longwall and tailgate for the succeeding 
one). Therefore, the entries must be kept open for the 
time it takes to mine two complete longwall panels. 
Single-entry longwall development was a solution to the 
strata problems experienced in Europe (6). 

European-type single entries are driven much as U.S. 
tunnels are driven, that is, undivided with mandatory 
auxiliary ventilation provided by intake or return air tubes 
or both. European mining regulations are much more 
stringent than U.S. regulations in some areas and less so 
in others. In Europe, all equipment in the single entry 
must be permissible and fireproof; however, only one 
escapeway is required. European law also restricts the 
number of miners working in the single entry, and fire 
protection measures tend to be more severe. 

Europeans use single entries to develop retreating and 
advancing longwalls for a number of important reasons: 



(1) They offer complete extraction of limited coal reserves, 

(2) they provide a method of limiting subsidence damage 
at the surface, and (3) they offer superior control of ex- 
treme ground pressures at great depth. When a mine is 
deep, an entry developed in solid coal will not stay open 
without excessive support maintenance. This phenomenon 
appears when depth exceeds a specific limit, which de- 
pends on the nature of the strata, coal strength, and 
pressure concentrations resulting from prior mining. This 
type of structural instability should be distinguished from 
localized roof falls. These instabilities are, of course, 
interrelated; however, structural instability will not always 
result in roof falls, but rather may cause a gradual closure 
of the opening. Pillars will yield or the floor will heave, 
restricting movement through the entry. In many cases, 
single entries are driven completely away from the coal 
seam in more competent rock, which results in less closure 
in the longwall development openings. 

Extreme rock pressure may also limit the use of 
retreating longwalls to cases where development entries 
remain usable throughout the life of the panel. When 
entries require excessive support maintenance, the primary 
consequences are that developments are made only as 
needed, not ahead of time, and the number of entries is 
kept to a minimum. The advantage inherent in driving a 
single entry comes from its geometric configuration. 
Stability is maintained because less ground is disturbed, 
chain pillars are not created, and the stress field of the 
surrounding area is uniformly distributed around the single 
opening. A secondary consequence is that when the total 
number of entries is kept to a minimum, more care can be 
given to supporting them. Wire mesh is bolted to the roof 
and walls, steel arches are set, and the cavity between the 
support and the stratum is filled. With this type of sup- 
port, maintenance of a single entry is less time consuming 
and less costly than for a multiple-entry development. 

There is a major difference between U.S. and European 
development philosophies. Generally, in Europe, entry 
development is considered a necessary, expensive invest- 
ment to open longwall panels. Coal is not produced dur- 
ing development since either rock is taken with the coal 



seam or the entry is driven entirely out of seam. This type 
of development is expensive, but in the long term, better 
returns on investment can be achieved. Very little coal 
must be left in place for support, and the maintenance of 
main entries is much less expensive because ground distur- 
bance during development is minimal. A coal property 
can be developed from a central location to its boundaries 
and production can then proceed inward, leaving the 
mined-out area behind. In this way, all the advantages of 
single entries-that is, rapid development, improved ex- 
traction ratio, improved subsidence control, and improved 
ground control-can be realized. U.S. mines, on the other 
hand, view the development stage as a coal-producing unit 
in its own right and therefore as profit generating. This 
disparity between U.S. and European strategies promotes 
two entirely different development approaches and results 
in a marked dissimilarity in the number and configuration 
of entries in development headings. 

Longwall panel development in the United States is car- 
ried out almost entirely in-seam, and multiple entries and 
crosscuts form rooms and pillars. European developments 
tend to be single entries driven out of seam with a large 
rectangular cross section or an arched roof if strata control 
is a problem. A width-height ratio of 3:2 is common (6). 
Haulage, ventilation, materials supply, and the escapeway 
are all contained in this one entry. Figure 1 shows a 
European-type single-entry development driven with a 
roadheader. 

The absence of a divider wall is the most striking differ- 
ence between U.S. and European single-entry systems. In 
order to drive the type of entry shown in figure 1, it is 
necessary to extract not only the coal, but a large amount 
of roof rock as well. Mining machines used to drive these 
entries must be able to cut rock as well as coal, and they 
must be permissible, a requirement placed on all equip- 
ment used in the entry. The main types used are road- 
headers, dintheaders, in-seam miners, and continuous 
miners. The types of strata to be cut are the deciding 
factors in choosing which piece of equipment to use. 



Continuous miners are used for coal and soft rock, but 
roadheaders and dintheaders are preferred for harder 
strata. These machines also have the ability to drive 
arched or high rectangular entries, while continuous 
miners are somewhat limited as to the shape they can 
produce. Much research has gone into the design of these 
types of machines, and they are available in a variety of 
configurations to fill different mining needs. 

One type of machine widely accepted and used in 
British mines is the partial cutting machine or in-seam 
miner. This type of machine drives a wide, low, elliptical 
entry and uses a continuous cutting operation. A dis- 
charge conveyor moves the cut coal from the back of the 
machine to the entry conveyor. The in-seam miner is used 
primarily in coal and soft rock and has the advantage of 
allowing immediate installation of supports while pro- 
ducing speeds of over 50 ft of advance per shift and gener- 
ating little dust. Disadvantages are that it does not cut 
hard material efficiently and it is difficult to steer (7). 

Longwall mining methods vary among the European 
coal-producing countries. British mine operators use more 
retreat mining, while West German mine operators favor 
advancing mining. In 1979, with over 400 operating long- 
wall faces in the Federal Republic of Germany, 58 pet 
were advancing, primarily because retreat mining is more 
costly because of prior entry development. Retreat mining 
does, however, offer the advantages of reconnaissance of 
the coalbed prior to mining, cooling and degassing of the 
strata along the road, and separation of entry advance 
work from the face production with alleviation of the 
inherent dust problem. The West Germans take advan- 
tage of these benefits, yet still control costs by employing 
a ventilation system that allows one gate road to be devel- 
oped prior to mining while the other is advanced with the 
face. 

Another method that is becoming popular is the alter- 
nate advancing and retreating panels. Face equipment 
may be moved straight across the gate entry to the next 
panel, avoiding costly delays incurred while moving heavy 




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Bridge conveyor Belt 



ELEVATION 




Exhaust ventilation 




WW// 

PLAN VIEW 




6 12 

i i i 

Scale, ft 
SECTION A-A 

Figure 1 .-Elevation and plan view of European-type single entry. 



equipment from the end of one panel to the start of 
another (8). 

West German engineers have persisted in their research 
on the optimum entry configuration for single entries. 
Arched entries approximately 16 to 20 ft wide and 12 to 
14 ft high predominate (6), particularly in the Ruhr 
District of the Federal Republic of Germany. Supported 
by yielding steel arches, these entries offer good strata 
control as well as provide adequate clearance for venti- 
lation requirements and for equipment needed for haulage, 
support, and transportation of personnel and materials. 
In mines with shallow depths and more favorable ground 
control conditions, rectangular entries are often used 
because support costs are less. Rectangular entries are 
generally lower than arched entries and are narrower at 
the roof than at the floor (so that they are actually a 
trapezoidal shape). 

In the 1960's, several experiments were conducted by 
the West Germans using in-seam miners to develop wide 
(up to 30 ft), rectangular, single entries. The objectives 
were to (1) increase space available in the entry to accom- 
modate larger mining equipment, (2) maximize support 
strength while minimizing convergence, and (3) obtain 
maximum support strength using at least four rows of 
props to divide the entry into three or more compartments 
(6). Even though the trials were conducted in what were 
considered to be favorable conditions, the test entries were 
subjected to excessive deformation caused by floor heave. 
This caused severe difficulties in repair and maintenance, 
eventually ending the experiment. The conclusion drawn 
was that entries with excessive width-height ratios were 
dangerous under the ground conditions found in European 
coal mines. This conclusion corroborates the experience 
of the first U.S. single entry, which had a cross section 
approximately 26 ft wide by 6 ft high. It, too, proved dif- 
ficult to maintain. 

Australian mine development is similar to U.S. devel- 
opment; that is, longwall mining is a relatively new 
method. It is not widely used outside of the South Coast 
District of New South Wales where mining conditions are 
considered difficult. Interest in longwall mining is growing, 
however, with several reasons listed by the Australian Joint 
Coal Board in its 34th annual report (1980-81) (9). These 
reasons included a recognition of the technological limita- 
tions of room-and-pillar mining with continuous miners, 
potential of increased size of mining operations using long- 
walls, improved coal recovery ratios, and safer working 
conditions. 

Australian longwall panels are currently developed with 
continuous miners driving multiple entries. Ellalong 
Colliery in New South Wales was the first to experiment 
with single entries, driving a 14.5-ft-wide by 5.5-ft-high 
entry in 1981 to help overcome severe ground control 
problems (10). This field trial was considered a success; 
a stable roadway was developed at advance rates exceeding 
those produced by dintheaders used in similar conditions. 

Although British mines have utilized longwalls and 
single entries for some time, one mine in particular used 
these techniques to solve a unique ground control problem. 



The West Yorkshire Coalfield in the Barnsley County area 
is considered one of the oldest industrialized coalfields in 
the world. As such, it is a labyrinth of worked-out seams 
and pillars. These pillars were left to control surface sub- 
sidence, protect underground roadways, control interaction 
between faces, and minimize the impact of faults within 
the coalbed. An estimated 100 million mt of "untouchable" 
coal was left underground, unminable because of the eco- 
nomic restraints of recovering such reserves using current 
technology. An additional complication is that the coal- 
field lies at shallow depths under a heavily populated area. 

The management of the South Kirby Colliery, one of 
the mines in the area, decided to try a single-entry retreat 
longwall system to mine protective pillars while main- 
taining their support capabilities. Using a Dosco 
dintheader to drive an entry 15 ft wide by 7 ft 2 in high, an 
experimental panel was developed. Although several 
design changes were made before driving a subsequent 
single entry, the experiment was considered a success, with 
substantial increases in production and profit. 

Among the benefits of using single entries for such 
applications are (1) the ability to mine under heavily 
populated areas with minimum surface damage and still 
maintain high productivity, (2) the ability to work seams 
prone to spontaneous combustion, (3) the ability to work 
old seams, recovering valuable reserves, and (4) the possi- 
bility of low-cost disposal of mine waste underground at 
the face (11). 

VENTILATION 

Ventilation practices and regulations in Europe differ 
from those in the United States. AIL including the United 
States, specify that as much air as necessary be delivered 
to the face to dilute fumes, dust, methane (CH 4 ), and 
other gases. U.S. regulations, however, specify a minimum 
quantity of air for a work area per unit of time, whereas 
French and West German laws regulate the amount of air 
required per person and unit of time. Air velocities are 
specified in terms of maximum allowable in the Federal 
Republic of Germany, France, and the Soviet Union, and 
as minimum required in Canada, Poland, and the United 
Kingdom. Minimums or maximums, however, are deter- 
mined largely by the function of the entry, whether a 
haulage route, development entry, head, or tailgate. Air 
velocities in the United States are specified in terms of 
minimum allowable for face ventilation and maximum 
allowable for trolley haulageways. 

Permissible methane levels vary, with a maximum 1.0 
pet by volume standard in all countries but Canada and the 
United Kingdom, which allow 1.25 pet. Allowable exemp- 
tions are given in all countries but Great Britain, with 
levels up to 2.0 pet (2.5 pet in Canada) return air from a 
bleeder system, where electrical equipment is absent, or 
where automatic shutoffs are present on all electrical 
equipment (6). Again, such exemptions depend on the use 
of the entry under consideration. 

When regulations on the ventilation of longwall oper- 
ations are compared, it is necessary to consider two 



separate cases-developing the entry and mining the long- 
wall panel. U.S. regulations allow permanent ventilation 
dividers to be used and require the installation of brattice 
line or similar device from the "last open crosscut" (a 
room-and-pillar mining phrase that defines the point where 
permanent ventilation controls end) to within 10 ft of the 
deepest penetration of the face (30 CFR 75.302-1, 1989). 
Auxiliary fans and tubing may be used in lieu of brattice 
systems; however, their use is controlled by the mini- 
mum air velocity and quantity of air required at the face 
(30 CFR 75.302-4, 1989). Regulations concerning inter- 
ruption of the primary ventilation system and scheduled 
idle periods, such as weekend and idle shifts, limit the 
practical distance that entries can be ventilated using 
auxiliary ventilation. Ventilation must be provided by the 
primary air current from the main fan during these peri- 
ods, thus auxiliary ventilation is only practical between the 
last open crosscut and the face, limiting its use to a dis- 
tance of a few hundred feet. 

European mining regulations, on the other hand, either 
restrict the use of permanent air dividers (as in the 
United Kingdom and the Soviet Union) or forbid their use 
entirely (France, the Federal Republic of Germany, and 
Poland). Development entries are ventilated instead with 
mandatory auxiliary systems. They may be operated over 
unlimited distances and may be blowing, exhausting, or 
combination fans connected to air ducts. Blowing-type 
systems generally predominate. This is very different from 
U.S. practice where regulations restrict the use of auxil- 
iary ventilation systems, that is, ventilation fans and 
tubing, as the primary means of ventilating a working area 
(30 CFR 75.302-4, 1989). 

One of the major differences between U.S. and 
European mining regulations, in regard to single-entry 
development, is the U.S. requirement that every working 
place must have at least two distinct, separately ventilated 
escapeways (30 CFR 75.1704, 1989). One must be in an 
intake air split and must not be used for belt or trolley 
haulage. Minimum width for this route is set at 6 ft. 
Because multiple entries are the rule in the United States, 
this requirement is usually met with no difficulty. It does, 
however, place a major constraint upon the use of single 
entries and precludes the use of European-style single 
entries altogether. Those single entries driven in the 
United States to date have complied with the law by 
driving one large entry and dividing it into two entries, 



using permanent, airtight center dividers. Escape doors 
were included at regular intervals in dividers. 

Ventilation during the production phase of longwall 
mining is basically the same in Europe and the United 
States, with the major difference found in the way the gob 
is ventilated. By law, abandoned workings must be sealed 
in every European country that uses single entries. U.S. 
law, on the other hand, requires them to be ventilated 
using a bleeder system or to be sealed only as a last resort. 
No other country requires ventilation of the gob. This is 
because in Europe methane buildup in the gob is not 
considered to be a problem because of the absence of 
large open cavities where methane could accumulate. If 
the gob is not ventilated, it is argued, spontaneous com- 
bustion is impossible because of the lack of oxygen, and 
other sources of ignition that could set off a fire are not 
present. In the rare case that a methane explosion should 
occur, the broken rock and dirt filling the gob would act as 
a protective barrier and extinguish any flame before severe 
damage was done. 

U.S. regulations require bleeder systems precisely 
because the large, open gob areas left when workings are 
mined out often become filled with gas. Bleeders are very 
effective in draining accumulated methane and controlling 
the problem of potential explosions. 

In summary, longwall mining, using single entries as 
gate roads has become the norm in major coal-producing 
countries other than the United States. By late 1983, an 
estimated 50 pet of the world's underground coal pro- 
duction was attributed to longwall mining (8). This is 
because of large potential productivity gains and because 
of the solutions it offers to problems inherent in un- 
derground mining. These problems include the mining 
of deep, gassy, unstable seams and/or the economic 
necessity of recovering reserves previously left to control 
subsidence or to protect subsequent work areas. The 
methods used to develop, ventilate, and support these 
entries, and to mine longwall panels have evolved in 
response to the varied situations and necessities ex- 
perienced. Consequently, legal requirements or restric- 
tions in other countries have developed specifically to 
control single-entry longwall mining. This is in sharp 
contrast to U.S. regulations concerning longwalls and 
single entries where regulations have been extended or 
adapted from legislation intended for underground room- 
and-pillar mining. 



U.S. SINGLE-ENTRY STUDIES 



Two single-entry development projects were conducted 
in the United States during the 1970's: the Sunnyside 
project at Kaiser Steel Corp.'s Sunnyside No. 1 Mine in 
Utah and the TBM project at EACC's Federal No. 2 Mine 
in West Virginia. The main similarity between the two 
projects was that they were single-entry drivages, divided 
to form two compartments to comply with coal mine safety 
regulations concerning ventilation, location of electrical 
equipment, and escapeways. Other than this, the two 



projects were different in many respects. A description of 
each of these projects will help to point out their simi- 
larities and differences, as well as problems that impede 
single-entry development in this country. 

SUNNYSIDE PROJECT 

The Sunnyside project was a 9-year research study, 
begim in 1971, that had the objective of determining 



whether a single entry supported down the center by a 
fire-resistant partition could be considered equal to or 
better than a double-entry system. The project was con- 
ducted under a cooperative agreement between Kaiser 
Steel Corp. and the Bureau's Spokane Research Center 
(SRC). Other participants included the Bureau's Denver 
Research Center and the U.S. Mine Safety and Health 
Administration (MSHA). 

The Sunnyside single-entry study was originally begun 
in the No. 2 Mine but was moved to the No. 1 Mine when 
several faults and an overlying minable coal seam were 
discovered at the original site. Several publications 
describe the early phases of this experiment (1, 12-13), 
and details of the project will not be described in this 
report. However, a few important points should be made. 
The new site was adjacent to several mined-out longwall 
panels, including one that had just begun production when 
the change in location was made (fig. 2). These panels 
were 4,500 ft long, 500 to 600 ft wide, and had an average 
seam height of 6 ft. An extensive study was made of the 
geology of the area in conjunction with the Sunnyside 
experiment. This study included diamond-drilled columns 
from the floor and roof of nearly 20 areas where ground 
movements were monitored. This geological information 
is available in a Bureau Report of Investigations (14). 

As originally planned, the purpose of the Sunnyside 
project was to study three major factors: ground control, 



ventilation, and safety procedures. Over 1,200 instruments 
were installed during the 9-year trial period. These instru- 
ments monitored roof-to-floor closure, entry deformation, 
and load on cribs, posts, and roof bolts, which were the 
primary supports used. A Bureau open-file report details 
the installation of the instruments and results of the 
monitoring efforts (15). 

Two longwall development headings were driven in con- 
nection with the project. The first heading began in May 
1973 and was driven a total of 4,500 ft. The first 1,500 ft 
was driven as a single entry followed by a 1,500-ft section 
of double entry. The final section was also completed as 
a single entry. This configuration allowed a good com- 
parison to be made between single- and double-entry 
behavior. The single-entry sections were 6 ft high and 
26 ft wide, divided down the center by a row of open wood 
cribs on 7-ft centers. A fireproof divider composed of 
steel panels coated with a fire-retardant sealant was 
attached to this crib line. Escape doors were installed 
every 100 ft to comply with regulations requiring access 
between escapeways. Fresh air was coursed to the working 
area on the left side of the divider and exhausted on the 
right. The conveyor belt was located in the exhaust air 
course, while the main supply and travel route was located 
in the fresh air course (16). 

Although no major problems were encountered, the 
first entry took 14 months to complete, which was longer 




Figure 2.-Sunnyside single-entry project 



than originally anticipated. The slow progress was due to 
many things, including an inexperienced crew and lack of 
adequate working space. The original plan was to have the 
bolter follow closely behind the continuous miner used to 
drive the entry. An MSHA regulation prohibiting more 
than one major piece of equipment operating on the same 
air split made this impossible, however. Consequently, 
whenever the mining machine finished a cut, it was 
trammed out and sat idle until the bolting crew finished. 
This also idled the shuttle car used to transport the cut 
coal to the section belt and resulted in a serious waste of 
labor. 

Another time-consuming operation was the construction 
of the center crib line and divider wall. A maximum of 
150 ft was allowed between the permanent divider and the 
face, with the line brattice used to divide and ventilate 
this area. As the face progressed further from the main 
haulageway, the amount of delay due to center wall 
construction increased. Crib blocks, metal panels, sealant, 
and all other supplies, such as bolting materials and spare 
parts, had to be brought into the entry by battery car. 
This proved to be slow and inefficient. The problem was 
compounded by the limited space in the entry itself. Only 
the intake half of the entry was available for transpor- 
tation, mining, and support functions. Progress was often 
impeded by lack of operating room. 

Ventilation was another problem. Metal landing mats 
were used in the bolting pattern to support the roof. They 
spanned the entry, making it very difficult for the divider 
wall to create an airtight seal. The divider wall itself was 
the source of many leaks. As the roof converged, it tended 
to break the sprayed sealant away from the wall, causing 
air leakage, and thus became a major maintenance prob- 
lem. Methane concentrations over the allowable 1.0 pet 
shut the section down repeatedly, requiring the crew to 
stop production and seal leaks, reroute brattice, or simply 
wait for the methane to dissipate. The use of auxiliary 
ventilation is required in most European mines, but is 
severely limited in U.S. mines in areas other than between 
the last open crosscut and the face. As the development 
face progressed further into the coal block, however, it 
became increasingly hard for the mine ventilation system 
to provide adequate air to the face, particularly in gassy 
areas. 

Advance rates for the 1,500-ft section of double entry 
showed some improvement over the first single-entry 
section. This was attributed to the crew's familiarity with 
the mining method and increased working space, as well as 
the elimination of the center wall. 

During the mining of the first longwall panel, it became 
obvious that the single row of wood cribs neither support- 
ed the entry adequately nor created a clean break line for 
the gob. Additional rows of cribs, as well as steel arches, 
wood posts, and steel beams, were used to maintain the 
entry, but in spite of the extra supports, it was often neces- 
sary to remove floor rock to provide adequate travel space. 
The maintenance cost to keep the entry open for use as a 
double gate made it obvious that the single entry, as 
designed, would not perform as desired. This realization 



brought about a redesign of the next single entry and the 
decision to test a new type of support. 

In April 1976, a 63-ft section of fiber-reinforced 
concrete cribs was installed about halfway into the first 
single-entry section. Wooden blocking materials were used 
between the concrete cribs and the roof to absorb initial 
loads and to ensure a tight fit to the roof. The concrete 
crib line (fig. 3) was very successful. Not only did that 
section of the entry maintain its original height without 
extra supports, but a clean break line was observed on the 
gob side, with little or no punching of the cribs through the 
roof, as was originally feared. 

The driving of the second 4,500-ft single entry was 
begun in September 1975 and completed in August 1976. 
This entry was designed to be used only as a headgate for 
a single longwall panel. No effort was made to hold it 
open to serve as a tailgate for the adjacent panel. This 
entry was 21 ft wide and was supported down the center by 
a row of wood posts on 4-ft centers (fig. 4). The usual 
bolting pattern supported the rest of the entry. A fire- 
resistant wall was constructed using metal panels attached 
to the posts and coated with a sealant (fig. 5). Metal 
escape doors were again installed every 100 ft. 

Advance rates for the second single entry were higher 
than the average for a two-entry system, and nearly double 
those achieved on the first single entry. Several factors 
contributed to this. The crew was more experienced, the 
support wall was simpler and easier to install, and 
alignment of the entry was accomplished using a laser gun, 
which simplified the process. Perhaps the two major dif- 
ferences, however, were changes in the haulage and 
ventilation systems. The shuttle car was replaced by a 
bridge conveyor from the back of the continuous miner to 
a walking tailpiece at the end of the belt (fig. 6). A maxi- 
mum of 120 ft could be mined before the tailpiece was 
advanced. Mine management estimated that this change 
alone improved single-entry advance rates 2.5 times (17). 

Ventilation was augmented using two auxiliary fans and 
fiberglass tubing. The tubing used for intake was equipped 
with a flexible endpiece so that air could be directed 
toward problem areas. Because of this dual system, there 
was little time lost because of forced work stoppages 
caused by high methane concentrations. 

A final cost comparison between the development of 
the Sunnyside single and double entries shows that, while 
advance rates were faster for a single-entry system, the 
overall cost was 42 pet higher than for a double-entry 
system (17). One reason for this was the higher productiv- 
ity rate for double entries (there is more coal to be ex- 
tracted, hence more production). The main reason, how- 
ever, was that the mining cycle only allowed one operation 
to occur at a time. Since the union did not allow mining 
machine operators to also operate bolting machines, work- 
ers and their equipment sat idle at least 50 pet of each 
shift. When labor costs make up an estimated 57 pet of 
the total production costs, it is easy to see why single 
entries driven with cyclic systems are not competitive (17). 

The Sunnyside single-entry project was considered a 
success by the Bureau in terms of reducing ground control 




Figure 3.-Concrete crib line in 17th L single entry. 



problems in deep coal mines. Many potential advantages 
of single entries were brought out by the trials. These 
advantages included reduction of bumps by eliminating 
chain pillars and decreasing the number of openings, faster 
development rates, elimination of problems caused by 
pillar remnants, extraction rates for panels approaching 
100 pet, reduction of methane emission from exposed ribs, 
and simplification of mining procedures due to straight- 
line development with no intersections. The major 
disadvantages listed by the Sunnyside Mine management 
were losses in productivity, increased costs to maintain the 
single entry as a tailgate, and the possibility that the center 
wall would fail to provide a smoke-free escapeway should 
a fire occur on the belt or equipment (17). 

An important point that should be noted when judging 
the success of the project is the marked improvement in 
the construction of the second single entry. Design 
changes necessitated by failures in the first panel devel- 
opment were successful in eliminating many of the early 
problems. This demonstrates the evolutionary process that 



will be necessary for the successful implementation of 
single-entry systems in the United States. 

TUNNEL-BORING MACHINE PROJECT 

The TBM project was proposed in 1971 by EACC. Its 
purpose was to test the technical and economic feasibility 
of developing coal mines with TBM's. The eventual 
demonstration was cosponsored by EACC and the 
Bureau's High Speed Coal-Mine Development Sub- 
Systems program. SRC served as principal investigator for 
the full term of the project, from 1974 to 1979, even 
though the program was transferred to DOE in 1977. 

The concept of using a TBM for driving develop- 
ment headings is a departure from the traditional U.S. 
development strategy discussed earlier with regard to 
European development methods. The TBM concept fol- 
lows the European strategy of developing a coal property 
from its center outward to its boundaries and then mining 
inward, leaving the mined-out areas behind. Mined-out 



10 







Figure 4.-Single-entry center wall in 18th L, right side. 




Figure 5.-Single-entry center wall In 18th L, left side. 



11 




ELEVATION 

Continuous miner Conveyor Belt 





12 



Scale, ft 



"^BI- 
SECTION A-A 

Figure 6.-Elevation and plan view of Sunnyside split single entry. 



areas are abandoned, so very little coal must be left in 
place for support. Maintenance of development headings 
is minimized because little ground is disturbed during 
development, and once an area has been mined out, the 
development headings may also be abandoned. This strat- 
egy is, of course, in conflict with present U.S. regulations 
regarding gob ventilation; however, its advantages cannot 
be overlooked, that is, rapid development, improved ex- 
traction ratio, improved subsidence control, and improved 
ground control. This strategy also allows flexibility in 
product control and, in gaseous mines, the degasification 
of the coal prior to mining (18). 

The site selected for the project was the Northeast 
Mains area of EACC's Federal No. 2 property where ear- 
lier attempts at conventional development had failed. 
Development of a 10-entry heading had been halted in the 
area some years before because of excessive methane. 
Although the high concentrations of methane presented 
special problems, successful implementation would prove 
that single entries could be driven in extremely gassy coal. 

At the time of the project, McGuire Corp. of Fort 
Smith, AR, operated the only permissible TBM in the 
country. The machine had been used to drive slopes down 
to coal seams and could be modified to drive in coal 
without going through the lengthy approval procedures 



required for new machines. McGuire was subcontracted 
by EACC, and preparation for the project began in 1974. 
The TBM was modified to excavate an 18-ft-diam tunnel 
a distance of 6,000 ft to intersect a shaft constructed for 
the project. 

The assembled TBM system was relatively complex for 
a coal mining operation (fig. 7). The basic machine con- 
sisted of a primary unit and a secondary unit. The primary 
unit included the cutterhead, loading buckets, roof bolters, 
and hydraulic gripping rams (wall grippers). The second- 
ary unit provided the electric and hydraulic power for the 
TBM system. The combined units were 50 ft long and 
weighed about 35 st. Immediately behind the secondary 
unit, a 50-ft skid-mounted trailing unit (tertiary unit) was 
used to provide the following support functions: (1) track 
installation, (2) application of shotcrete, and (3) divider 
support beam installation. The trailing unit was equipped 
with a monorail and air-powered cranes to handle heavy 
equipment and materials. 

The primary, secondary, and trailing units included steel 
panels dividing the tunnel entry into upper and lower com- 
partments (fig. 8). Steel divider panels also trailed these 
units for a distance of 320 ft to an automatic mine-car 
loading station. These sliding steel dividers carried the 
primary haulage system-an extendable conveyor formed by 



12 



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Operator's station 

Figure 7.-Tunnel-boring machine. 



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Shotcrete system 



Tunnel boring machine 




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PLAN VIEW 





SECTION SECTION 
A-A B-B 



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Scale, ft 



Figure 8.-Elevation and plan view of TBM split single entry. 



13 



two belts. Permanent concrete panels, called flexicore, 
were installed beneath a raised portion of the temporary 
divider just ahead of the loading station. Together, the 
sliding steel and the flexicore provided a continuous, 
horizontal divider from the entrance of the tunnel to the 
face. Ventilation air was directed through the lower com- 
partment to the face and exhausted through the upper 
compartment. Ten-ton mine cars were loaded at the load- 
ing station on a specially designed double-track carriage 
called a California switch. This unit was 390 ft long with 
a 40-ft ramp up from the main track. The California 
switch followed the TBM as it advanced by riding on the 
main track. The entire TBM system was approximately 
790 ft long when fully extended, but could collapse to 
about 540 ft when the loading chute and California switch 
were moved up. This was done at approximately 250-ft 
intervals. 

The TBM was a system designed to excavate, support, 
and construct the tunnel in one continuous operation. Ad- 
ditional support operations were carried out between the 
trailing unit and the front end of the California switch. 
Within this area, service lines were installed, degasification 
holes were drilled, and a 3-in layer of shotcrete was ap- 
plied to the walls. Two roof bolting machines located on 
the primary unit provided all the immediate roof support 
that was necessary. Installation of the flexicore divider 
took place from atop the California switch, beneath a 
raised portion of the sliding steel divider. It was antic- 
ipated that such a system would be capable of 100 ft of 
advance per day, as had been accomplished with TBM sys- 
tems used on civil engineering projects. Actual advance 
rates, however, were much lower because of a number of 
operational, design, and labor problems. 

Boring began in January 1976 with only the primary and 
secondary units in operation. As the TBM advanced, the 
trailings sections of the system were added until the entire 
system was assembled. Boring with the complete system 
did not begin until January 1977. The length of time taken 
to assemble the total system was a reflection of the prob- 
lems incurred in making the system comply with mining 
regulations. 

The final contract report concerning the TBM project 
(18) gives an account of the problems associated with the 
project from start to finish. Many of these problems were 
associated with equipment design or failure and with labor 
or management issues. The major concerns, however, in- 
volved the single-entry aspects of the project. Fire pre- 
vention is essential in any single entry, raising questions of 
electrical permissibility. In Europe, all equipment within 
a single entry must be permissible. This was the primary 
difference between European regulations and U.S. prac- 
tices concerning equipment. Other differences were in- 
fluenced either directly or indirectly by the determination 
of where permissible equipment would be allowed. In 
both the Sunnyside and the TBM projects, the last open 
crosscut was generally determined by MSHA to be the end 
of the permanent dividers. In the case of the TBM 
project, however, a decision was made not to allow non- 
permissible equipment within the mouth of the tunnel. 



This effectively made the tunnel mouth the last open 
crosscut. The one exception to this rule was the use of 
nonpermissible battery-powered locomotives in the tunnel 
behind the end of the permanent dividers. This allowance 
was granted by MSHA because no permissible locomotives 
were available and their construction would have been very 
costly and would have delayed the project by many 
months. 

The decision to use only permissible equipment in 
the tunnel affected another critical area. Because of the 
length of the entry, the operating voltage (480 V) could 
not be carried to the machine by a cable of practical size. 
It was necessary to use a transformer on the secondary 
unit to reduce the primary mine voltage of 7,200 V to 
480 V. Permissible transformers are not uncommon, but 
one using 7,200- V, l,000-kV»A primary power had never 
been built. In addition, 30 CFR 18.47 (d) (5) implies 
that face voltage shall not exceed 4,160 V. During the 
initial boring phase, a 480-V trailing cable was used while 
boring the 725-ft length required to assemble the com- 
plete system. Concurrently, a variance was sought under 
30 CFR 18.47 (d) (6), which allows MSHA to approve 
high-voltage equipment, provided additional safeguards are 
met. Many delays occurred during the approval process. 
Initial testing of a 7,200- to 480-V transformer at the 
Westinghouse High Power Laboratory in Pittsburgh, PA, 
led to improvements and eventual approval. 

Equipment permissibility is, of course, required in 
underground coal mines because of the explosive atmos- 
phere created by the generation of coal dust and the lib- 
eration of methane. In addition to permissibility, the 
amount of dust and methane in the ventilating air was also 
strictly regulated. The Northeast Mains area at the 
Federal No. 2 Mine had an established history of pro- 
ducing excessive methane. That area of the mine had al- 
ready been involved in a degasification project with the 
Bureau's Pittsburgh Research Center, so a degasification 
plan was devised to incorporate the tunnel into the existing 
system. The plan was to drill holes angled into the coal 
ahead of the tunnel face and vent the methane through a 
6-in pipeline and a borehole to the surface. These 3.5-in 
holes were drilled into alternating ribs at 250-ft intervals 
as soon as the trailing unit had passed and were angled 
20° from the tunnel centerline to place them ahead of the 
face. 

Many problems were encountered with the degasifica- 
tion system and it was eventually abandoned. As in the 
Sunnyside project, auxiliary face ventilation was used to 
control methane liberated during excavation. Several "hot 
spots" were encountered in the tunnel that halted work 
until the methane level was reduced, particularly toward 
the end of the project when advance rates were high. The 
most important control measure used, however, was apply- 
ing shotcrete to the tunnel walls, which sealed the coal 
from the atmosphere and prevented contamination of the 
intake air before it reached the face. Methane liberation 
in gaseous coal mines will always present a special prob- 
lem in single entries and will require that some type of 
sealant be used or that other measures be taken. 



14 



Another ventilation problem common to both the 
Sunnyside and the TBM projects was leaks in the divider 
between the intake and return airways. Because of the 
experimental nature of the TBM project, MSHA required 
that 50,000 cfm of intake air be supplied to a control point 
behind the trailing unit. Early in the project, it was 
recognized that maintaining this airflow would be a prob- 
lem, and a detailed ventilation study was begun (19). The 
study concluded that there would be sufficient airflow to 
complete the tunnel only if leaks in the divider could be 
controlled. The major sources of the leaks were cracks 
between the members of the permanent dividers and poor 
seals around air-lock doors in the dividers. Leaks were 
sealed on a continual basis throughout the project, but 
even so, only 50 pet of the air entering the single entry 
actually reached the face. This is considered a major 
obstacle to this type of single-entry arrangement. If multi- 
compartment single entries are to be used, improvements 
in methods of sealing divider walls will be necessary. 

Another major obstacle to the TBM project was the 
divider wall construction. As discussed earlier, the split 
single entry was developed as a means of driving a single 
entry while at the same time complying with the CFR and 



State mining laws concerning separate escapeways from 
each working area. For a divider wall to serve as a 
substitute for a line of chain pillars and stoppings, it has to 
prevent a fire or explosion on either side of the divider 
from propagating to the other side (30 CFR 75.329-2). 
This meant that the divider wall had to be built from sub- 
stantial materials. The divider wall was also required to 
have doors spaced every 100 ft to allow workers to pass 
from one side to the other. Most of the doors were 2 by 
2 ft, but every fifth door was much larger and had a stair- 
way that would allow an injured worker to be carried 
through on a stretcher (fig. 9). 

An industrial engineering study conducted for the 
Bureau identified the installation of the divider wall as the 
most time-consuming task in overall tunnel construction. 
Therefore, the divider wall not only created problems with 
ventilation, but its construction would have controlled the 
TBM excavation rate had it not been for many other un- 
scheduled delays. During the Sunnyside project, the divid- 
er wall created ventilation problems and its construction 
was a major obstacle to rapid development of the entry, 
particularly because of the difficulties encountered while 
bringing construction supplies in, but also because of the 








Figure 9.-Lower compartment of entry developed by TBM. 



15 



time used to build the wall, during which no mining 
occurred. Experience gathered from both projects has 
shown that divider wall construction and maintenance will 
be major obstacles to the efficient driving of split single 
entries. 

The single-entry projects in the United States have 
provided valuable experience to the mining industry. The 



most obvious lesson was that in order to bring European 
single entries into compliance with U.S. law, changes 
were made that created problems in construction and 
ventilation. These problems muted the primary reasons 
for single-entry development, that is, improved ground 
control, rapid development, and greater overall safety 
under severe mining conditions. 



OTHER SINGLE-ENTRY RESEARCH STUDIES IN UNITED STATES 



Two other studies initiated by the Bureau have contrib- 
uted significantly to single-entry research in this country. 
The first of these studies was conducted by NAMCO and 
resulted in a report entitled "Single-Entry Longwall Study" 
(6). The second was a study of the design of a single-entry 
development system for retreat longwall mining systems, 
conducted by Ketron. These and several other related 
studies will be discussed briefly in the following sections. 

NORTH AMERICAN MINING CONSULTANTS STUDY 

The purposes of the NAMCO study were threefold: 
first, to identify State and Federal regulations that con- 
strain driving longwall development panels; second, to 
propose optional single-entry layouts and mine designs; 
and third, to compare costs between the proposed designs 
and conventional panel development. 

This study concluded that true single-entry devel- 
opments are prohibited by current regulations. Under 
30 CFR 75.1704 and 30 CFR 75.1704-1 (1989), every active 
workplace is required to have two separate escapeways, 
one of which must be located in intake air. The laws of 
several states as well as 30 CFR 75.302 (1989) control the 
use of auxiliary ventilation systems and limit their use to 
the working face. Since 1970, 30 CFR 75.326 (1989) has 
prohibited the use of belt conveyors in intake or return air 
passages, limiting their installation to separate compart- 
ments carrying reduced airflows. Two other regulations, 
30 CFR 75.316-2 and 30 CFR 75.311 (1989), restrict the 
use of single entries for longwall panel development by 
requiring bleeder systems for mined panels and by pro- 
hibiting any intake air containing more than 0.25 pet 
methane from passing a gob area if it is to be used to 
ventilate an active working face. For both the Sunnyside 
and TBM projects, regulations prohibiting the installation 
of belt conveyors in return air were waived under a grand- 
father clause, and the separate ventilation and escapeway 
requirements were met with the split-entry arrangement. 

The NAMCO study also compared the mining laws of 
the United States with those of other countries, high- 
lighting the relative merits of each. Three longwall panel 
development systems were compared: a multiple-entry sys- 
tem, a European-type single-entry system, and a modified 
system of NAMCO's own design that was a compromise 
between European practices and U.S. requirements. The 
modified system failed to satisfy all U.S. regulations, but it 
was similar to the modified single entries driven at 
Sunnyside. This study concluded that in the absence of 



adverse geological conditions, the multiple-entry systems 
required by U.S. laws and regulations are inherently safer 
than single-entry systems. The study also noted that where 
the physical conditions become hazardous for the multiple- 
entry method of working, those U.S. laws and regulations 
that constrain or prohibit European-type single-entry 
workings negate their purpose and are of doubtful benefit. 
In such cases, European regulations, methods, and experi- 
ence, which are drawn directly from more hazardous con- 
ditions, offer a method of single-entry operation that 
provides improved control over the strata and greater 
overall safety (6). 

NAMCO's economic comparison also favored the 
multiple-entry system when used in conventionally devel- 
oped mines. A case was made, however, for the economic 
benefits of single-entry development for an entire mine 
property. The central argument was that increased re- 
source recovery could offset the higher capital cost of 
single entries. 

KETRON STUDY 

The purpose of the Ketron study was to analyze the 
single-entry demonstrations conducted in the 1970's and to 
design an improved, legally acceptable single-entry system 
for developing retreat longwall panels. The resulting con- 
cept was another modified system based on an entry split 
into three separate compartments: an intake airway, a 
return airway, and a belt compartment in the center of the 
entry. The proposed system would be similar to a three- 
entry room-and-pillar system and thus would comply with 
current regulations, provided favorable interpretations con- 
cerning the divider walls were applied. This system would 
meet those regulations that presently constrain or prohibit 
driving two-compartment, split single entries, as well as 
true single entries. The regulations dealing with bleeders 
and fresh air could also be met with this configuration. 

The Ketron design recommended a class of European 
continuous mining systems generally referred to as "partial 
cutting machines" and specified the Eickhoff short-face 
ranging shearer as the best alternative. This system is an 
advancing "mini-longwalT system with a standard longwall 
shearer riding an armored face conveyor. A stage loader 
feeds a belt conveyor, providing continuous haulage. This 
system can drive a single entry between 20 to 40 ft wide. 
Roof bolters are mounted on the mining machine for 
immediate support. The Ketron design called for a 30-ft- 
wide entry. Additional support for this span would come 



16 



from two divider walls constructed to form a three- 
compartment system. The key to supporting such a wide 
span would be to prevent as much roof convergence as 
possible before installation of the support walls. The 
Eickhoff system would allow the walls to be constructed to 
within 12 ft of the cutting face. 

The primary advantages of the Ketron entry design 
would be in meeting the regulatory requirements and in 
providing a truly continuous mining system. As long as the 
divider walls were interpreted as adequate substitutes for 
chain pillars and stoppings, regulations would be the same 
as for three-entry systems. The delays and loss of produc- 
tivity associated with the Sunnyside single entry would be 
superseded by the total system approach provided by the 
Eickhoff continuous miner. The apparent disadvantages 
are that two divider walls must be constructed and sealed 
and that these walls must be strong enough to support a 
30-ft span. Several wall designs were evaluated in the 
study. The most desirable design consisted of a yielding 
steel post for support, wire mesh for lagging, and fiber- 
reinforced resin as a sealant. Based on the TBM and 
Sunnyside projects, the construction and maintenance of 
these walls would be an impediment to rapid, efficient 
driving of this type of entry system. The concept delivered 
by the Ketron study is, however, a significant improvement 
over past U.S. single-entry systems. Questions remain to 
be answered, particularly with regard to the support of a 
30-ft roof span, the construction of the divider walls, and 
MSHA's interpretation of regulations concerning the split 
single entries. Many of these questions could be answered 
only by carrying out a field demonstration similar to the 
Sunnyside and TBM projects. 

RESEARCH RELATED TO SINGLE ENTRIES 

During the 1970's, there were many additional studies 
undertaken in support of single-entry research or to inves- 
tigate related subjects. Many of these studies dealt with 
new types of instruments such as the Creare vibrating- 
wire stress gauge (20) or with new equipment such as the 
Dosco in-seam miner (21-22). Other studies, funded 
under contract by the Bureau, produced computerized 
two-dimensional (23) or three-dimensional, finite-element 



analyses of the Sunnyside single entry, based upon the data 
obtained during the trial. One finite-element analysis 
compared the theoretical stability of several different entry 
configurations, including the single entry (24). 

Another Bureau study using the single-entry concept at 
Sunnyside involved installing a flexible steel liner in an 
advancing tailgate and monitoring it from November 1976 
to March 1977. The liner provided a temporary second 
escapeway and return air conduit for the 15th R longwall 
panel. It was made up of 4-ft-diam, 4-ga steel sections 
bolted together and installed immediately behind the 
second longwall support, which was a combination of 
chocks and shield supports. An inert cushion was used as 
a base for the liner, which was usually buried 2 ft in the 
bottom. The first 50 ft were protected by a double row of 
wood cribs, but thereafter the liner's only protection came 
from wood posts and broken rock hand shoveled over it. 
Six stations were monitored in the 992-ft liner to measure 
deformation. As a result of information gained during this 
study, the Bureau funded a contract to design and demon- 
strate a more permanent liner (25). 

Another aspect investigated was divider-support walls. 
Initially, different materials for construction of divider 
walls were evaluated (26), and later a rapid center wall 
placement system was designed using foam concrete as the 
construction material (27). There were also investigations 
into the economic and safety aspects of divider wall 
systems (28). Divider wall research led to a Bureau proj- 
ect to design and test concrete cribs. These concrete crib 
blocks not only proved to be much better supports than 
their wooden counterparts, but they also were lighter, 
cheaper, and easier to install (29). Field tests of two crib 
block configurations were held in conjunction with the 
Sunnyside project, and two more designs were tested at 
five other U.S. mines (30). As a result of that research, 
concrete crib blocks are being manufactured commercially 
and are being used more often underground. 

Many other projects not directly related to single-entry 
research were associated with the Sunnyside and TBM 
demonstrations. These demonstrations merely provided 
convenient in-mine laboratories for investigating new 
hardware and mining concepts. 



CONCLUSIONS 



The four projects described in this report— the Sunnyside 
project, the TBM project, the NAMCO study, and the 
Ketron single-entry design-have had a great impact on 
single-entry research in this country. The Sunnyside and 
TBM demonstrations were different in purpose and design; 
however, they established the compartmentalized entry as 
the U.S. answer to the single entry. Although the 
NAMCO study raises some serious questions about the 
effectiveness and relative safety of this type of system, 
both the NAMCO study and Ketron design used this basic 
concept in their proposals for future single entries. The 



divided single-entry concept was not selected for its 
simplicity or its efficiency, nor was it selected because of 
improved ground control or safety. It was selected be- 
cause it is more easily adapted to U.S. mining regulations. 
Divided single entries have been driven and used with- 
out mishap, but their productivity and economics have not 
been attractive. Difficulties have arisen in adapting single 
entries to U.S. mining laws. Mining regulations, both State 
and Federal have evolved over the years to govern room- 
and-pillar mining and limit the introduction of new and 
different mining methods. Single entries, for example, 



17 



were possible only after obtaining variances from statutes 
regarding permissibility and by liberal interpretation of 
regulations dealing with ventilation seals and fire barriers. 
In the United States, ventilation and escapeway 
regulations have forced the use of a divider wall. For a 
divider wall to be in compliance with mining law, however, 
it must not allow the propagation of either a fire or an 
explosion from one side to the other. The Sunnyside and 
TBM projects set the precedent for entry development 
using a divided single entry. For longwall panel devel- 
opment, where the most critical need exists, the Sunnyside 
project demonstrated that, although the entries were suc- 
cessfully driven and used, the more conventional two-entry 
system was preferable. Construction and maintenance of 
the divider wall and lost productivity caused by cycling 
equipment at the face made these entries too costly. 

The Ketron design is indicative of the next generation 
of divided single entries, and while a systems approach to 
the design has eliminated delays caused by rotating work- 
ers and equipment at the face, the three-compartment con- 
cept requires doubling the construction time and widening 
the entry span. This three-compartment design will be 
necessary to comply with current U.S. regulations in all 
coal mines except those where grandfather clauses permit 
the operation of conveyors in return airways. In addition 
to these unsolved problems, a major safety question is at 
issue with the divided single entry: Are divider walls 
actually barriers to fire and explosion as is mandated by 
30 CFR 75.329-2 (1989)? 

Single-entry development in the United States is far 
from perfected. Many problems remain unsolved, such as 
how to control excessive amounts of methane in gassy 
areas. Experiences to date have demonstrated that the 



problems are not insurmountable, however, and that they 
can be solved by ingenuity and careful engineering. The 
pertinent questions for now concern the future of the 
single entry in this country. Is there a need for this meth- 
od right now? Will there be a need for it in the future? 
The general consensus of nearly all the single-entry inves- 
tigators is that although the economics and efficiency of 
the modified U.S. single entry are not attractive, they do 
provide additional stability in deep mines. Kaiser Steel 
Corporation management said in assessing the Sunnyside 
experiments (77): "It has been proved that a single entry 
can be driven in less time with no diminution of safety to 
the face crew. Future mining, under deeper cover and less 
competent roof, could easily swing the tide of opinion 
toward the single-entry concept." 

If single-entry technology is needed, what direction 
should it take? One direction leads to further devel- 
opment of the divided single entry in order to comply with 
Federal and State regulations regarding ventilation and 
escapeways. The other direction leads to the adoption of 
European technology and its attendant regulations. 

Further development and refinement will surely be 
necessary to make divided single entries meet current min- 
ing regulations and be economically attractive. European 
single-entry systems will not comply with U.S. regula- 
tions; however, years of experience with these systems 
have proven them to be safe and efficient longwall devel- 
opment techniques under European conditions. In the 
end, the future of single entries in this country will be 
decided by industry needs and further reconciliation of 
regulatory concerns and the technical and economic merits 
of single-entry systems. 



REFERENCES 



1. Poad, M. E., E. L. Phillips, and E. T. Bowers. Single-Entry 
Development for Longwall Mining. Paper in First Symposium on 
Underground Mining (Louisville, KY, Oct. 21-23, 1975). Nat. Coal 
Assoc., Washington, DC, v. 1, 1975, pp. 135-143. 

2. Jackson, D. Advancing Longwall Mining: A First for Mid- 
Continent Coal and a First for the U.S. Sec. in Coal Age Operating 
Handbook of Underground Mining. Coal Age Min. Inf. Services, 
McGraw-Hill, New York, v. 1, 1977, pp. 62-67. 

3. Bullers, W. E Boring a Coal Mine Slope. Min. Congr. J., v. 63, 
No. 5, 1977, pp. 4(M3. 

4. Brezovec, D. Roadheader Drives Two Slopes. Coal Age, v. 88, 
No. 8, 1983, pp. 50-52. 

5. Adam, F. J. Special Monitoring Requirements for Multi-Lift 
Longwall Mining Field Trial (DOE contract DE-AC01-79ET11268, Task 
Order 123). Dep. Energy, July 1982, pp. 6-9. 

6. North American Mining Consultants, Inc. Single-Entry Longwall 
Study, v. 1: Final Report (DOE contract DE-AC01-77-ET-12558). 
Dep. Energy, 1982, 242 pp.; NTIS DE 82019861. 

7. Tucker, R H. Mining Development in the National Coal Board. 
Min. Eng. (London), v. 142, No. 260, 1983, pp. 589-598. 

8. Bordia, S. K. Design of Longwall Mining Systems. Colliery 
Guardian, v. 231, No. 10, 1983, pp. 521-523. 

9. Australian Coal Miner. Joint Coal Board Releases Its Annual 
Report Covering 1980/81. V. 4, No. 4, 1982, pp. 34, 42, 46-48. 

10. Wallman, D., and J. McKendry. Single-Entry Development at 
Ellalong Colliery. Mine and Quarry Mechanisation, 1981, pp. 67-74. 



11. Round, C. The Design of the Experience With Single-Entry 
Faces at South Kirby Colliery. Min. Eng. (London), v. 142, No. 253, 
1982, pp. 193-199. 

12. Poad, M. E., G. G. Waddell, and E. L. Phillips. Single-Entry 
Development for Longwall Mining. Research Approach and Results at 
Sunnyside No. 2 Mine, Carbon County, Utah. BuMines RI 8252, 1977, 
29 pp. 

13. Poad, M. E, G. G. Waddell, and M. D. Ross. Research Program 
for Single-Entry Longwall Development of Coal Mines. Paper in 
Proceedings 1974 Rapid Excavation and Tunneling Conference (San 
Francisco, CA, June 24-27, 1974). AIME, New York, v. 2, 1974, 
pp. 1471-1472. 

14. Scheibner, B. J. Geology of the Single-Entry Project at Sunnyside 
Coal Mines 1 and 2, Sunnyside, Utah. BuMines RI 8402, 1979, 106 pp. 

15. Bowers, E. T, and L. N. Henton. A Summary of Data From the 
Sunnyside Single Entry Study-1971-80. BuMines OFR 25-84, 1983, 
541 pp. 

16. Ross, M. D. Longwall Mining Using the Single-Entry System and 
Advancing Tailgate. Min. Congr. J., v. 60, No. 8, 1974, pp. 38-41. 

17. Huntsman, L. W., and D. C. Pearce. Entry Development for 
Longwall Mining. Min. Congr. J., v. 67, No. 7, 1981, pp. 29-32, 51. 

18. Tisdale, J. E., and D. R Skidmore. Demonstration of Tunnel- 
Boring Machine for Coal-Mine Development: Final Technical Report 
(DOE contract ET-74-C-01-9068, East. Associated Coal Corp.). Dep. 
Energy, 1979, 149 pp.; NTIS DE 82013516. 



18 



19. Belton, A. Ventilation Analysis. Final Report to Eastern 
Associated Coal Corp. From John T. Boyd Co., 1978; available upon 
request from M. O. Serbousek, BuMines, Spokane, WA. 

20. Van Dillen, D. E. The Three-Dimensional Structural Analysis of 
Double-Entry and Single-Entry Coal Mines. Final Report. Volume III. 
Three-Dimensional Finite Element Analyses of Single- and Double- 
Entry Portions of Sunnyside Mine No. 1 (contract H0262020, Agbabian 
Associates). BuMines OFR 16 (3)-80, 1978, 278 pp.; NTIS PB 80- 
150360. 

21. Tokarg, R D., K. Hay, C. B. Conrad, J. P. Haskins, and J. J. 
Jacobsen. In-Mine Test and Economic Evaluation of the Dosco In- 
Seam Miner (DOE contract ET-76-C-06-1830). Dep. Energy, 1980, 
101 pp. 

22. Manley, C. D. Demonstration and Evaluation of Dosco In-Seam 
Heading Machine: Final Report (DOE contract ET-76-C-01-9044, 
Allied Corp.). Dep. Energy, 1979, 28 pp.; NTIS DE 82004520. 

23. Pariseau, W. G. Interpretation of Rock Mechanics Data (Vol. I) 
(A Two-Dimensional Finite Element Approach to the Evaluation of 
Underground Coal Mine Stability) (contract H0220077, Univ. UT). 
BuMines OFR 47 (l)-80, 1978, 172 pp. 

24. Van Dillen, D. E., and R W. Fellner. Comparisons of Structural 
Stability for Entry Configurations and Ground Support for Longwall 



Panel Development (contract J0285014, Agbabian Associates). BuMines 
OFR 50-82, 1981, 225 pp.; NTIS PB 82-201864. 

25. Ko, K. C. Flexible Liner for Use in Advancing Tailgate (contract 
H0292014, Kenneth C. Ko & Associates). BuMines OFR 6-82, 1980, 
191 pp.; NTIS PB 82-149352. 

26. Poad, M. E., M. O. Serbousek, and J. Goris. Engineering Proper- 
ties of Fiber-Reinforced and Polymer-Impregnated Shotcrete. BuMines 
RI 8001, 1975, 25 pp. 

27. Marshall, M. D. The Evaluation of Foam Concrete for a Rapid 
Centerwall Placement System: Final Technical Report (DOE contract 
ET-75-C-01-9101, MSA Res. Corp.). Dep. Energy, 1978, 68 pp.; NTIS 
HCP/T9101-01. 

28. Walton, D. R, S. B. Rondum, P. W. Kauffman, and S. A. 
Hawkins. Health and Safety Analysis on Support Walls, Volume 1 
(contract J0295036, Manage. Eng. Inc.). BuMines OFR 121(l)-82, 
1980, 207 pp.; NTIS PB 82-251950. 

29. Anderson, G. L., and T. W. Smelser. Development, Testing, and 
Analysis of Steel-Fiber-Reinforced Concrete Mine Support Members. 
BuMines RI 8412, 1980, 38 pp. 

30. Smelser, T. W., and L. N. Henton. Concrete Crib Design and 
Field Testing. BuMines RI 8804, 1983, 44 pp. 



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